The present invention relates to a gateway digital loop carrier device provided between an integrated access device and a switch that have interfaces different from each other.
FIGS. 11A and 11B are diagrams showing a conventional subscriber oriented network. Referring to FIGS. 11A and 11B, a remote digital terminal (RDT) is connected to a local switch (Central Office (CO)) via a digital transmission facility such as optical fibers and so on.
The remote digital terminal is located farther than the central office and accommodates subscriber terminals such as telephones etc. that cannot be accommodated directly in the central office in terms of a problem of distance. The remote digital terminal is based on Telcordia (previously called Bellcore) TR-008 defined as one of the switch interface (interconnection interface) standards (the remote digital terminal based on TR-008 will hereinafter be referred to as “TR-008RDT” as the case may be). On the other hand, the switch is also based on TR-008.
The TR-008RDT converts signals on 96 telephone subscriber lines at the maximum into digital signals DS0s (Digital Signal level 0). Then, the TR-008RDT clusters the converted signals DS0 for every 24 subscribers, multiplexes these signals into four lines (five lines including a protection line) of DSX-1 or T1 signals (DS1) at the maximum, and carries the DSX-1 or T1 signals via the digital transmission facility to the central office. TR-008 basically adopts a fixed time slot allocation scheme between the switch and the RDT.
Over the recent years, the switch and the RDT based on TR-303 or GR-303 as a standard substitute for TR-008 has been spreading (the RDT based on TR/GR-303 will hereinafter be referred to as a “TR/GR-303RDT” as the case may be) for the purposes of efficiently utilizing transmission path bandwidth, doing a standardized operation and management and expanding the subscribers.
The TR/GR-303RDT allocates (time slot allocation) 2048 telephone lines at the maximum to 28 lines of DSX-1 or T1 signals (DS1) at the maximum by a line concentration function. A main target of the service provided by this TR/GR-303RDT is a voice service. Architecture of the network to which the TR/GR-303RDT is applied is much the same as architecture of the network to which the TR-008RDT is applied.
By the way, there has recently increased a demand for data (packet) communications on the Internet, and a remote digital terminal called an integrated access device (IAD) is developed. The integrated access device is a small capacity (one DSX-1 or T1 at the minimum, i.e., 24 DS0s at the minimum) type remote digital terminal that receives data and conventional telephone services.
The integrated access device is generally installed in a small business office steering clear of installing a large capacity device but requiring a predetermined or wider transmission bandwidth. All the integrated access devices support TR-008 as a switch interface.
TR-303 was developed for the purpose of accommodating a multiplicity of subscribers, and hence, if the device implements TR-303, it is required that large-scale and complicated hardware and firmware be incorporated therein. By contrast, an implementation of TR-008 can be actualized by small-scale and simple hardware for firmware.
The integrated access device has only architecture for accommodating telephone (including modem) and ISDN subscribers that implement TR-008, and for connecting these subscribers to the switch supporting TR-008. Namely, the integrated access device supports only TR-008. Therefore, as shown in FIG. 11B, it was unfeasible to provide the service from the switch to the telephones and others by mutually connecting to the switch supporting only TR/GR-303.